This invention relates to a gas-blast switch for interrupting an electric arc struck across a pair of stationary and movable contact members by blowing an arc extinguishing fluid such as sulfurhexafluoride (SF.sub.6) against the electric arc, and more particularly to a self-arc-extinguishing type switch utilizing an arc-extinguishing fluid at high pressure on an electric arc struck across a pair of stationary and movable contact members for extinguishing the electric arc.
Among puffer type switches for extinguishing the electric arc struck across the stationary and movable contact members by blowing the arc-extinguishing fluid such as sulfur hexafluoride against the electric arc, here have been known switches of the type including a pair of engageable contact members arranged to be separated from each other within an arc-extinguishing chamber of a predetermined volume to strike an electric arc thereacross and an amount of an arc-extinguishing fluid disposed in the arc-extinguishing chamber to be expanded by the thermal energy of the electric arc thereby to increase in pressure after which the arc-extinguishing fluid from the arc-extinguishing chamber is delivered to the exterior thereof when the spacing between the contact members reaches a predetermined magnitude, whereupon the resulting stream of the arc-extinguishing fluid is caused to interrupt the electric arc.
Switches of the type referred to are called self-extinguishing type switches because the arc-extinguishing operation is performed by utilizing the arc-extinguishing fluid having the pressure increased by the arc energy.Those switches have eliminated the necessity of providing additional means for pressurizing the arc-extinguishing fluid which have been required for conventional puffer type switches so that the resulting structure is simple and economical.
On the other hand, switches of the type referred to sometimes do not satisfactorily pressurize the arc-extinguishing fluid for interrupting low currents because the resulting arc energy is low. In order to avoid this problem, Japanese laid-open patent application No. 25,869/78, for example, discloses a pressurizing piston disposed in an arc-extinguishing chamber to interlock with the operation of separating a pair of contact member from each other thereby to pressurize the arc-extinguishing fluid. The piston is arranged to be moved over the entire volume of the arc-extinguishing chamber to compress the arc-extinguishing fluid. Therefore, when interrupting a high current having high arc energy, the arc-extinguishing fluid is greatly increased in pressure when its temperature rises excessively resulting in the deterioration of the interrupting performance. Also the arc-extinguishing chamber becomes extremely small in volume because of the movement of the piston as described above and therefore a very high fluid pressure is created. This has resulted in the necessity of using high-power operating means for operating the piston as well as the necessity of providing closing means having a high power sufficient to overcome the force generated by the operating means.
If the fluid pressure within the arc-extinguishing chamber overcomes the force for operating the piston then the piston is moved toward its initial inoperative position. This has resulted in a reduction in fluid pressure within the arc-extinguishing chamber and therefore in interrupting performance. With the piston is formed integrally with the stationary contact member, the movable contact member may repeatedly engage with and disengage from the stationary contact member resulting in the occurrence of chattering. Under these circumstances, if electric arcs strike across both contact members then the contact members may be fused to each other.
Accordingly, it is an object of the present invention to provide a new and improved self-extinguishing switch having excellent interrupting performance by increasing the pressure of the arc-extinguishing fluid so that it is suitable for interrupting currents within a wide range of from a low to a high magnitude thereby to exert a puffer action on the electric arc struck across a pair of stationary and movable contact members.
It is another object of the present invention to provide a new and improved self-extinguishing switch capable of interrupting current efficiently even though the current is low.
It is still another object of the present invention to provide a new and improved self-extinguishing type switch having a long time interval during which an arc-extinguishing fluid is blown against the electric arc.
It is a different object of the present invention to provide a self-extinguishing switch having improved interrupting characteristics for high currents while retaining the good interrupting performance for low currents.
It is another object of the present invention to provide a new and improved self-extinguishing type switch capable of reserving a proper amount of arc-extinguishing fluid having increased pressure up to the time of interruption of the electric.
It is another object of the present invention to provide a new and improved self-extinguishing type switch including means for controlling the temperature rise of the arc-extinguishing fluid and maintaining a pressure thereof as high as possible.
It is another object of the present invention to provide a new and improved self-extinguishing type switch for preventing a pair of stationary and movable contact members from being fused to each during the closing operation without any deterioration in interrupting performance.
It is a separate object of the present invention to provide a new and improved self-extinguishing type switch including simplified operating means and having a stablized interrupting performance.